I don't have any covers but use a 'makedo' as I often use the yak as a 'cartop carrier' for carrying all sorts of clothing(in garb. bags), boots, wetsuits, pfds etc.

I just turn a spare (or the only) sprayskirt upside down, put it on the yak, gather all the loose neoprene tightly in my left hand, pull up and wind a bunch of line around the gather and tie it off. Turn right side up and put on the yak after all the stuff is in. Quite a few driving rainstorms and maybe only small amts of water in. Certainly nothing to be seen.4-5hrs hiway speed.

I take it off and unload after driving. Unsuitable for long times in UV light etc.

-mick